## Building GEOS From Source

### Prerequisites

GEOS has no external library dependencies and can be built with any C++11
compiler.

### Unix

GEOS can be built on Unix systems using either the autotools or CMake build
systems.

#### Using Autotools:

When building GEOS using autotools, a `configure` script must first be generated
using the `autogen.sh` file included in the root of the repository:

    ./autogen.sh

An out-of-tree build can then be initiated by creating a subdirectory and
running the generated `configure` script from that subdirectory:

    mkdir obj && cd obj && ../configure

Once the `configure` script has run, GEOS can be built by running `make` and
installed by running `make install`. The test suite can be run using `make
check`.

#### Using CMake:

To build `GEOS` using CMake, create a build directory and run the `cmake` command
from that location:

    mkdir build && cd build && cmake -DCMAKE_BUILD_TYPE=Release ..

Setting `CMAKE_BUILD_TYPE` to `Release` is necessary to enable compiler
optimizations.

Once the `cmake` tool has run, GEOS can be built by running `make` and
installed by running `make install`.

The entire test suite can be run using `make check`.
Alternatively, the `ctest` command can be used, which provides more control over test execution.
For example, `ctest -R unit-capi -j2` uses a regular expression to run all tests
associated with the C API, using two processes in parallel.
A list of available tests can be obtained using `ctest -N`.

### Microsoft Windows

GEOS can be built with Microsoft Visual C++ by opening the `CMakeLists.txt` in
the project root using `File > Open > CMake`.

If you prefer the command-line

#### Build with CMake generator for Ninja (fast)

In the Visual Studio 2019 command prompt, `x64 Native Tools Command Prompt for VS 2019` or `x64_x86 Cross Tools Command Prompt for VS 2019`:

```
cmake -S . -B _build_vs2019_ninja -G Ninja -DCMAKE_BUILD_TYPE=Release
cmake --build _build_vs2019_ninja -j 16 --verbose
```

#### Build with CMake generator for MSBuild (default)

In the non-specific Command Prompt:

##### 64-bit

```
cmake -S . -B _build_vs2019x64 -G "Visual Studio 16 2019" -A x64 -DCMAKE_GENERATOR_TOOLSET=host=x64
cmake --build _build_vs2019x64 --config Release -j 16 --verbose
```

##### 32-bit

```
cmake -S . -B _build_vs2019x32 -G "Visual Studio 16 2019" -A x32 -DCMAKE_GENERATOR_TOOLSET=host=x64
cmake --build _build_vs2019x32 --config Release -j 16 --verbose
```

#### Test using CMake

```
cd <build directory>
ctest --show-only
ctest
ctest --output-on-failure
ctest -V
ctest -VV
```